Highly integrated high-speed optical switches and matrix switches are in high demand by the modern optical communications and information processing systems, industrial automatic control systems, test & measurement instrumentation and optical signal sensing systems. As the information and data capacities in applications are rapidly increasing, the scalability, density and integrity of optical switches and matrix switches are prominent trends. Planar lightwave circuit (PLC) technology is widely accepted for manufacturing integrated photonic components and silicon-on-insulator (SOI) waveguides and has attracted growing interest for implementing the highly integrated high-speed PLC-based optical and photonic switching devices. SOI-based PLC (SOI-PLC) technology has shown merit in photonic circuits capable of tightly integrating passive and (hybrid) active devices. However, so far only a few reports have been published on the subject of low port-count optical matrix switches on SOI-PLC platforms that exploit slow thermo-optic switch elements that have electrical power-hungry heating elements.
The overall suitability of SOI-PLC technology in manufacturing both active and passive highly integrated photonic devices and systems, and the compatibility of the SOI-PLC technology with complementary metal oxide semiconductor (CMOS) technologies makes it possible to manufacture SOI-based photonic integrated device products with commercially acceptable costs, and further form the hybrid integration of micro photonics and microelectronics on a single chip.
Deployment of free-electrons and holes injection/depletion to implement electro-optic (EO) modulation of the nanosecond level was pioneered with the silicon and SOI-PLC optical modulators as described in G. V. Treyz et al., “Silicon Mach-Zehnder waveguide interferometers based on the plasma dispersion effect,” Appl. Phys. Letter Vol. 59, pp. 771-773 (1991) and A. Liu et al. “A high-speed silicon optical modulator based on a metal-oxide-semiconductor capacitor,” Nature, Vol. 427, pp. 615-618 (2004). All aforementioned EO modulated devices, irrespective of switches and modulators, based on free-carrier injection/depletion plasma-dispersion-effect, are combined with Mach-Zehnder interferometer (MZI) waveguide configurations, so several intrinsic drawbacks or difficulties one may face are mainly a few centimeters of interaction length (L) between the electric field and optical signal, and a 3-5V drive voltage Vπ for a phase shift of π between two arms of the MZI configuration due to the intrinsically required VπL of this MZI modulation regime. Such high drive voltage and device length are not only a negative consequence of a high-speed operating device, but the long transport path and high electric current also directly or indirectly cause high optical loss though some effective optimal approaches have been deployed to improve the modulation efficiency with a relatively small VπL value. In addition, the large footprint size and drive voltage of MZI based switching cells seriously restrict the R&D actions and applications of silicon photonics technology. However, the SOI waveguide, as a fundamental element of all the passive and active functional devices and systems based on a SOI-PLC platform, has achieved an acceptable level in several critical performance aspects including the optical transport loss, the carrier injection/depletion based EO modulation, and the compatibility with the conventional electronic manufacturing technology.
Therefore, it is desirable to develop a micro-size optical switch on a SOI-PLC platform that will have switching speed at nanosecond level, low optical access loss, and low polarization dependent loss. This section provides background information related to the present disclosure which is not necessarily prior art.